The present invention relates generally to rotatable members that are able to achieve balanced conditions throughout a range of rotational speeds. The present invention also relates to methods and systems for dynamically balancing rotatable members through the continual determination of out-of-balance forces and motion to thereby take corresponding counter balancing action. The present invention additionally relates to methods and systems in which inertial masses are actively shifted within a body rotating on a shaft in order to cancel rotational imbalances associated with the shaft and bodies co-rotating thereon. The present invention additionally relates to methods and system for dynamic balancing utilizing concurrent control actuator actions.
Mass unbalance in rotating machinery leads to machine vibrations that are synchronous with the rotational speed. These vibrations can lead to excessive wear and to unacceptable levels of noise. Typical imbalances in large, rotating machines are on the order of one inch-pound.
It is a common practice to balance a rotatable body by adjusting a distribution of moveable, inertial masses attached to the body. Once certain types of bodies have been balanced in this fashion, they will generally remain in balance only for a limited range of rotational velocities. A tire, for instance, can be balanced once by applying weights to it. This balanced condition will remain until the tire hits a very big bump or the weights are removed. A centrifuge for fluid extraction, however, can change the amount of balance as more fluid is extracted.
Many machines are also configured as freestanding spring mass systems in which different components thereof pass through resonance ranges until the machine is out of balance. Additionally, such machines may include a rotating body flexibly located at the end of a shaft rather than fixed to the shaft as in the case of a tire. Thus, moments about a bearing shaft may also be created merely by the weight of the shaft. A flexible shaft rotating at speeds above half of its first critical speed can generally assume significant deformations, which add to the imbalance. This often poses problems in the operation of large turbines and turbo generators.
Machines of this kind usually operate above their first critical speed. As a consequence, machines that are initially balanced at relatively low speeds may tend to vibrate excessively as they approach full operating speed. Additionally, if one balances to an acceptable level rather than to a perfect condition (which is difficult to measure), the amount of remaining balance will progressively apply force as the speed increases. This increase in force is due to the fact that F xcex1 rxcfx892, (i.e., note that F is the out of balance force, r is the radius of the rotating body and xcfx89 is its rotational speed).
The mass unbalance distributed along the length of a rotating body gives rise to a rotating force vector at each of the bearings that support the body. In general, the force vectors at respective bearings are not in phase. At each bearing, the rotating force vector may be opposed by a rotating reaction force, which can be transmitted to the bearing supports as noise and vibration.
The purpose of active, dynamic balancing is to shift an inertial mass to the appropriate radial eccentricity and angular position for canceling the net mass unbalance. At the appropriate radial and angular distribution, the inertial mass can generate a rotating centrifugal force vector equal in magnitude and phase to the reaction force referred to above.
Many different types of balancing schemes are known to those skilled in the art. When rotatable objects are not in perfect balance, nonsymmetrical mass distribution creates out-of-balance forces because of the centrifugal forces that result from rotation of the object. Although rotatable objects find use in many different applications, one particular application is a rotating drum of a washing machine.
U.S. Pat. No. 5,561,993, which issued to Elgersma et al. on Oct. 22, 1996, and is incorporated herein by reference, discloses a self-balancing rotatable apparatus. Elgersma et al. disclosed a method and system for measuring forces and motion via accelerations at various locations in a system. The forces and moments were balanced through the use of a matrix manipulation technique for determining appropriate counterbalance forces located at two axial positions of the rotatable member. The method and system described in Elgersma et al. accounted for possible accelerations of a machine, such as a washing machine, which could not otherwise be accomplished if the motion of the machine were not measured. Such a method and system was operable in association with machines that are not rigidly attached to immovable objects, such as concrete floors. The algorithm disclosed by Elgersma et al. permitted counterbalance forces to be calculated even though a washing machine is located on a moveable floor structure combined with carpet padding and carpets between the washing machine and a rigid support structure.
U.S. Pat. No. 5,561,993 thus described a dynamic balance control algorithm for balancing a centrifuge for fluid extraction. To accomplish such balance control, mass was placed sequentially in the back and front planes and mathematical model and balancing algorithm thereof was developed, such that the dynamics of the system were divided into two columns based on whether mass was placed in a front plane (i.e., column 2) or the back plane (i.e., column 1) of the spinner. A matrix was thus calculated utilizing multiple rows based on force and acceleration measurements and parameters before and after a prior control action. Each counterbalance mass correction depended on a prior control action or injection.
A counterbalance procedure was developed wherein a known quantity of water or fluid mass was separately injected at known positions within the system. Acceleration and force measurements were taken to determine the degree of perturbation caused by the injections. That perturbation, along with further sensor measurement, was utilized to determine the required correction counterbalance that would place the rotating assembly in a balanced condition. After each counterbalance injection was made, its perturbation effect was used as a test injection for the next counterbalance calculation. Thus, the prior perturbations created by the latest counterbalance could be utilized under many conditions for purposes of determining the next location and magnitude for a counterbalance injection. Such a technique for balancing a rotating system or apparatus did not, however, permit fluid mass to be simultaneously placed in multiple (e.g., front and back) planes of the system in order to perform counterbalance actions and measurements necessary to place the system in a balanced state.
Based on the foregoing, it can be appreciated that previous methods for dynamically balancing a rotatable member have experienced limitations in the degree of balance that can be achieved, the time to acquire balance, and in the rotational speeds under which they are workable. It has, therefore, become apparent to the present inventors that it would be desirable to correct imbalances in a dynamic rotatable self-balancing apparatus or rotating system, such as a washing machine, for example, utilizing concurrent control actuator actions exemplified by simultaneous front and back axial plane injection techniques.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention, and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is one aspect of the present invention to provide methods and systems in which rotatable members can achieve balanced conditions throughout a range of rotational speeds.
It is another aspect of the present invention to provide methods and systems for dynamically balancing rotatable members through the continual determination of out-of-balance forces and motion to thereby take corresponding counter balancing action.
It is still another aspect of the present invention to provide methods and system for dynamic balancing utilizing concurrent control actuator actions or simultaneous injections.
The above and other aspects are achieved as is now described. Methods and systems are disclosed herein for balancing a rotating system having a rotatable member and a shaft attached to the rotatable member. Balancing is generally based on a system response to control actions accomplished through the concurrent actuation of multiple control actuators (e.g., simultaneous injections) for placing mass at predetermined locations within the rotating system. Fluid mass can be simultaneously injected at predetermined locations within the rotating system. A matrix of measured force and motion parameters can then be calculated in response to simultaneously placing mass at predetermined locations within the rotating system, in order to determine a required correction necessary to place the rotating system in a balanced state. Force can be measured at predetermined locations within the rotating system in response to simultaneously injecting the fluid mass at the predetermined locations within the rotating system.
Motion (e.g., acceleration) can also be measured at predetermined locations within the rotating system in response to simultaneously injecting the fluid mass at predetermined locations within the rotating system. The matrix of measured force and motion parameters can be calculated based on independent perturbations of the rotating system.
An independence or rank criterion, implemented as a complex vector angle criterion for the case of two perturbations to the rotating system, can also be utilized to determine whether each consecutive injection is different enough from the previous injection (i.e., can excite the system in an independent direction) to form a model that is sufficiently representative of the dynamics of the rotating system. Additionally, the complex vector angle between two test vectors or the rank of a matrix containing more than two test vectors can be calculated based on a rank criterion of a matrix containing one or more test vectors.